linux-kernel - Re: process hangs on do

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Date:	Thu, 25 Oct 2012 11:57:19 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Qiang Gao <gaoqiangscut@...il.com>
Cc:	Balbir Singh <bsingharora@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
	linux-mm@...ck.org
Subject: Re: process hangs on do_exit when oom happens

On Wed 24-10-12 11:44:17, Qiang Gao wrote:
> On Wed, Oct 24, 2012 at 1:43 AM, Balbir Singh <bsingharora@...il.com> wrote:
> > On Tue, Oct 23, 2012 at 3:45 PM, Michal Hocko <mhocko@...e.cz> wrote:
> >> On Tue 23-10-12 18:10:33, Qiang Gao wrote:
> >>> On Tue, Oct 23, 2012 at 5:50 PM, Michal Hocko <mhocko@...e.cz> wrote:
> >>> > On Tue 23-10-12 15:18:48, Qiang Gao wrote:
> >>> >> This process was moved to RT-priority queue when global oom-killer
> >>> >> happened to boost the recovery of the system..
> >>> >
> >>> > Who did that? oom killer doesn't boost the priority (scheduling class)
> >>> > AFAIK.
> >>> >
> >>> >> but it wasn't get properily dealt with. I still have no idea why where
> >>> >> the problem is ..
> >>> >
> >>> > Well your configuration says that there is no runtime reserved for the
> >>> > group.
> >>> > Please refer to Documentation/scheduler/sched-rt-group.txt for more
> >>> > information.
> >>> >
> >> [...]
> >>> maybe this is not a upstream-kernel bug. the centos/redhat kernel
> >>> would boost the process to RT prio when the process was selected
> >>> by oom-killer.
> >>
> >> This still looks like your cpu controller is misconfigured. Even if the
> >> task is promoted to be realtime.
> >
> >
> > Precisely! You need to have rt bandwidth enabled for RT tasks to run,
> > as a workaround please give the groups some RT bandwidth and then work
> > out the migration to RT and what should be the defaults on the distro.
> >
> > Balbir
> 
> 
> see https://patchwork.kernel.org/patch/719411/

The patch surely "fixes" your problem but the primary fault here is the
mis-configured cpu cgroup. If the value for the bandwidth is zero by
default then all realtime processes in the group a screwed. The value
should be set to something more reasonable.
I am not familiar with the cpu controller but it seems that
alloc_rt_sched_group needs some treat. Care to look into it and send a
patch to the cpu controller and cgroup maintainers, please?

-- 
Michal Hocko
SUSE Labs
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